Shallow Water, Deep Miocene Play

There was mystery and a lot of unanswered questions surrounding the mega-deep Blackbeard West well that spudded early in 2005 at South Timbalier Block 168 on the shallow water Gulf of Mexico shelf.

As tight holes go, this may have been as tight as any has been in industry history, spawning rampant rumors and speculation as it headed for a near-world-record target depth of 38,000 feet in the quest for ultra-deep gas (>25,000 feet).

The well spudded during the time when the shallow water deep gas play (15,000 to 25,000 feet) was essentially the domestic exploration event of the moment.

Some of the savvier deep gas players met with success and continue playing this trend today, while others faded from the picture after a few costly unproductive deep holes.

As for that eagerly anticipated ultra-deep test at Blackbeard, the project has been on hold since August 2006, when the Blackbeard West well was temporarily abandoned by operator ExxonMobil. The well reached a measured depth of 30,067 feet, reportedly running up a tab somewhere above $200 million.

Enter seasoned shallow water deep gas player McMoRan Exploration.

The company acquired the rights to the Blackbeard project when it purchased the Newfield Gulf of Mexico shelf properties in 2007.

This past March McMoRan re-entered the Blackbeard West well, which sits in 70 feet of water. The plan is to drill to a proposed total depth of 31,267 feet to evaluate the deeper targets – and possibly deepen the hole to as much as 33,000 feet.

At press time, the drill bit had reached 27,000 feet.

The Rowan Gorilla IV rig is drilling the well for operator McMoRan and partners Plains Exploration and Production Co. and Energy XXI (Bermuda).

It’s all about the deep Miocene rocks, something near and dear to the heart of veteran geologist James Moffett, co-chairman of the board at McMoRan – he’s quick to say, “I cut my eye teeth doing work onshore in the deep Miocene.”

32 Prospects, 17 Discoveries

It was a natural progression to ultimately move onto the shelf to apply the deep Miocene exploration techniques honed in the onshore environment.

In fact, McMoRan assembled exploration rights to 1.5 million gross acres to pursue hydrocarbons in the deep Miocene geological trend beneath historical or existing production in shallow waters. So far, they have racked up 17 discoveries on 32 prospects drilled since 2004.

“The importance is not only have we found production, but we’re able to see these wells flow at rates substantially higher than the Plio-Pleistocene,” Moffett said. “There, an average well would be 10 million (cubic feet) a day, and a big one would be 20 to 25, but we’re getting completions that flow at 30 to 60.”

A production test announced in early April for the company’s Flatrock #2 well at South Marsh Island indicated a gross flow rate of approximately 103 mmcf/d, 1,890 b/d of condensate and no water. The well was drilled in 10 feet of water and bottomed out slightly deeper than 18,000 feet.

When the shallow water deep gas play first kicked off, many prospectors were concerned about the quality of the sands in the deeper pressured reservoirs.

“We knew from onshore they had a lot of gas,” Moffett said. “Below the geopressure there was high quality sand that had good flow rates in the Planulina, Hollywood, Hackberry – to name a few of so-called deeper gas (reservoirs) onshore – and we’ve been able to confirm those kinds of quality sands do exist on these deep structures.

“If you’ve got the structure and the high quality sands with the high flow rates, that’s what will make these deep wells feasible,” he said. “Blackbeard is just a continuation of the same concept.

“The ultra-deep play at Blackbeard is to test to see if the same sands exist even deeper than our original deeper gas sands concept as you go out into the deeper part of the shelf,” he said.

The intrepid explorer emphasized that even though the current modern day shelf is what everyone sees, it had no impact on Miocene deposition.

“The controlling feature for Miocene deposition in the Gulf Coast was the shelf at Miocene time, which was north of the current coastline,” Moffett said.

“If you draw a line along the shelf edge today and move it back to the north and put it onshore you can see all of a sudden that all of this deepwater deep gas and shelf deep gas (sands) were being deposited in the same Miocene basin just off the mouth of the Mississippi River, which is the source of all the sand.”

A Stratigraphic Test?

Moffett noted the shelf play they have been drilling is in what they call the traditional trapdoor normal fault tectonics, which occurred in an extension type pressure regime, whereas the deep gas fold belt that’s been delineated in the deep water is more of a compressional feature.

“The geological style changes at about 25,000 feet, and you go below the traditional tectonics of the deep gas play I’ve been playing,” Moffett said, “and you go into the fold belt of the Miocene that’s been basically calibrated out in the deepwater.”

Moffett noted that the structures seen in the traditional deep gas play can be quite large – as much as 3,000 to 5,000 acres, which they think may apply to Flatrock. But the structures in the deep water and what appear to be the same structures and same age rocks in the ultra-deep (play) are substantially larger – 10,000 to 15,000 acres.

The discoveries reported at fields such as Thunder Horse, Mad Dog and others are in deep water, but the sands are the same age as what appears to be in the ultra-deep section on the shelf, according to Moffett.

In a sense, Blackbeard might be considered to be a stratigraphic test. The structures can be seen via 3-D data, so the challenge is to confirm that the prolific deep sands from the deepwater gas play do, in fact, exist underneath the shelf.

“Logic says they should, because all the sands, we believe, came from the Mississippi River to the north,” Moffett said.

“If they’re in deepwater, some of them had to come across the shelf – that’s our play in a nutshell.”

For now, intrigue is the name of the game.

“Until we get in the new hole and test our concepts and prove these sands exist or if there was some barrier to deposition, everybody has to hold their breath,” Moffett said.